Fathoms Below
by AppleCiderr
Summary: A battle against an unknown adversary goes sour, and an explosion causes the world to believe Tony Stark died to save them all. In reality, Tony Stark has been transformed by the very thing he was trying to subdue, and finds himself now a part of the bottomless blue.
1. Chapter 1

The fight had been chaos from the beginning, but with the new rules that the accord put up, they could only be called if it _was_ chaos. This was no exception, in fact it was even worse than normal. The man had started by attacking New York, creating explosions and knocking down buildings. Tony, Vision, and Rhodey responded immediately while Peter helped evacuate the citizens.

As they followed after their new enemy, Tony turned on his coms and declared,"No attacking, just try and distract him. We need to figure out how to subdue his powers before he can get near civilians again."

After gaining affirmative responses, Tony flew forward, staring at the yellow glow that surrounded the figure with utter confusion. "Friday, can you analyze that glow?" He asked, causing data to instantly appear on the screen.

"Of course, boss," The AI responded,"I'll start analyzing it right away." Tony silently thanked his creation before flying back into the battle.

Thankfully, they had managed to chase the man off the mainland and over the ocean, but he was continuing to go farther out to sea. Something seems suspicious.. About how willing he was to let them force him out to sea.

Finally, the man stopped, returning to a standing position. The staff within his hands was suddenly pointed at all of them, sending blasts of the yellow light towards them. The three scrambled out of the way, taking different positions around the figure. From his closer position, Tony could see his eyes were glowing the same color, before being thrown back in order to avoid another blast.

 _Something about the powers he is using.. Where have I see this before?_ He thought curiously, dodging another blast as he shot back with his repulsor. His mind flew into action, desperately trying to remember what made it so familiar..

 _It doesn't make sense.. I've only ever seen abilities like this with people who were exposed to.._ Suddenly, everything clicked in his mind. "The Tesseract.." He whispered.

"Tony?" Rhodey worriedly called,"What did you say?!" The genius jolted out of his thoughts, scrambling to a stop and looking over the group.

All his logic seemed to fade away from him, his mind flashing back to all the horror the tesseract had caused. _Loki, the Chitauri, HYDRA, Ultron…_ His mind was clawing, screaming, desperately begging for it all to end. _No more! No more! I have to get it away from him!_

Tony flew forward, slamming into the man who had been focused on Vision. He jerked out, yelling violent as he scrambled to hold on to the staff. Rhodey and Vision attempted to fly forward, desperate to help their friend, but the yellow lights continued to explode and shoot out in different areas. They pulled away, narrowly avoiding each blast.

They continued to fly around, desperately dodging and looking for a way in. But the two kept fighting, the man trying to keep Tony from grabbing hold of the stone while Tony looked for any way to get it.

Suddenly, the man lifted the staff, pressing it against Tony. Just as it began to glow, Tony grabbed the top of it with one metal hand. "Tony! Stop!" Rhodey yelled desperately, flying forward to separate the two, but he was too late.

Suddenly, a huge explosion of light filled his vision. The impact sent Rhodey and Vision flying back, scrambling to regain their flight before they could fall into the vast ocean below. Rhodey's blurred eyes struggled to regain sight after the blast that invaded it, while all the sensors in the War Machine screeched out and struggled to stay online.

When his vision finally cleared, he saw a large cloud of nearly translucent smoke that was slowly descending down towards the water below. But the yellow glow was gone, as were the two men who had been battling just moments before.

Terror balled up in Rhodey's gut as he stared out at the vast . "T-Tony?! TONY?!" He cried, his wide brown eyes frantically scanning the ocean for any sign of his best friend. Out of the corner of his eyes, he saw red. Quickly turning around, he caught sight of the man they had just been battling moment ago. His body was covered with blood, body parts floating around. Rhodey couldn't tell if he was breathing, but he didn't care. If he had gotten that injured from the explosion.. Then what happened to Tony?!

"Rhodes, look," A monotone voice softly called, causing the man to whip around just in time to see something floating up to the surface of the water. _Tony!_ Rhodey instantly thought, lifting his faceplate, flying down in order to help his best friend back to shore. As he got closer though, he realized what it was.

Floating out of the water was not his best friend.. It was broken shards of the Iron Man suit, with water soaked blood flowing down into it. Horror sent Rhodey's stomach dropping, as he whispered,"No… NO!"

He whipped around towards the android, who was staring at the shards of metal with wide eyes. "Vision!" He cried,"W-we have to call Ross! Get a ship out here! He can't be dead! We can find him!"

Vision quickly grabbed the colonel and firmly said,"Rhodey, we have to go back to the city to help. We just have to accept that Tony isn't coming back."

Rhodey wanted to argue, to claim that Tony may have survived, but with the condition that bastard was in, he didn't know if he could have. He lowered his head, tears beginning to fall from his eyes, before he wrenched his eyes into flight.

"Let's go," He whispered, bursting into flight back towards New York. He didn't look back, he _couldn't_ look back.

He couldn't face the reality that his best friend was gone forever.

* * *

It was hours later, in the darkness of the ocean, that two gentle glows could be seen. One was a dull yellow, while the other was a bright blue shine. There, unmoving on his side, was the unconscious form of Tony Stark.

Suddenly, his eyes twitched, a groan escaping him as he began to shift. His hands went to his eyes, desperately trying to rub out the throbbing pain he felt. _What happened..?_ He wondered _. I was fighting.. Everything hurt… And then what?_ It didn't feel like he was in the hospital. _Where am I?_

Finally, the genius managed to force his heavy eyelids open. Instead of the bright lights and white walls of the hospital, he found himself staring at the rippling water above him, and the fish floating around him. _I'm underwater..?_ He thought, confusion filling his overloaded brain.

Suddenly, the dam broke, and Tony felt panic explode through him. _I'M DROWNING!_ He thought in horror, Afghanistan painfully coming back into his mind once more. Tony instantly began thrashing, throwing himself around in attempt to reach the surface.

It took several moments for Tony to realize that he wasn't choking on the water. In fact, he was breathing just fine. He froze, before beginning to breathe in and out. Again, he was breathing .perfectly. He frowned deeply, his hands rubbing at his temples while he desperately tried to understand what was going on.

As the genius continued rubbing, he realized that there was a strange feeling on his hands. Tony frowned, pulling them back, and looking at them. His brown eyes widened, staring at the sight of blue specs on his hands. _Scales?_ He croaked internally, his brain beginning to panic again. _Why do I have scales?!_

Tony frantically began to rub down his arms, feeling speckles of scales all the way down. _This doesn't make sense! Why would I have these?!_ But as he tried to sit up, he froze. Then, the genius realized something he hadn't noticed earlier.

He couldn't feel his legs.

When Tony's wide brown eyes turned to look down at his lower body, desperately looking for what the next anomaly could possibly be, he realized that the reason he couldn't feel them was because he didn't _have_ any.

What he _did_ have, however, was a long, blue mermaid tail.


	2. Chapter 2

Tony stared at the tail for several long, tense seconds. Then, he reached leaned forward, grabbing the end of the tail and attempting to pull it closer. He felt sudden pain, and quickly leg go. Instead of trying to grab it, he instead attempted to move it around. Sure enough, it flopped against the ground, sending sand floating into the water. It was the same glow as his tail, but with some good scales speckled across it.

The genius released a nervous laugh, his hands threading into his hair. "A tail.." He whispered,"I have a tail…"

All the anxiety that had suddenly been building up his his chest suddenly exploded out, as he threw his hands up and screamed,"WHAT THE FUCK IS GOING ON?!" His exclamation sent many of the curious fish that had been surrounding him scurrying away in a panic.

Tony ignored them, placing his hands on his head again, closing his eyes and releasing many deep breaths. "Okay… Think.. Don't just panic, think," He ordered himself,"How could this have happened? What could have done this to me?"

His mind went over everything, and he could only come to one solution. The stone, the one that Friday said had a signature much like the tesseract. Instantly, he came to awareness again. Whipping around, he saw a gentle yellow glow near him. There was the stone, it's glow was much duller than before, but sure enough it was there.

 _I have to get it back to the surface._ Tony thought instantly. _Then we can try to change me back, and lock it away._

He tried to stand, before remembering. "Oh yeah, tail," He muttered in slight annoyance, raising it up and down. "How do I work you?"

In the corner of his eye, he noticed something moving closer to the yellow gem. It was a crab, who was nudging it with it's pinchers. Then, it started trying to pick it up. Tony let out a frantic noise, pushing himself off the sand and frantically trying to swim.

"Hey! Hey!" He exclaimed,"Don't touch that! Leave it alone!" The crab jumped as he flopped down next to him, pulling the stone and the sand with it away from the creature.

The crab quickly scurried away, but not before Tony could hear him grumble. "Alright!" It snapped,"Jeez, what's a crab gotta do to eat?"

Tony stared after the crab, and then slammed his head down in the sand with a muffled moan. "I don't think I can take much more of this.." He mumbled,"I need to find Rhodey, they've gotten be looking for me!"

The genius rolled over, brown eyes looking toward the surface above him. _But.. How do I get up?_ He wondered, looking down at the blue tail once more. He huffed, poking at it in frustration, tweaking one blue scale. "I guess Howard was wrong, Disney movies would have taught me a valuable lesson," He muttered with sarcastic amusement.

Tony then shook those thoughts away, thinking about other animals with horizontal tales instead of vertical ones. "Whales and Dolphins do.." He thought, remembering how those animals would move whenever he took the time to watch them.

The genius then took a deep breath, and shut his eyes, before pushing himself off the ocean floor. Instantly, he began moving the blue tail up and down. He remained tense, and slowly opened his eyes to see that instead of falling back down, he was moving up. Instantly, his brown eyes filled with excitement, a smile crawling up his face.

He moved the tail just the slightest, and remained in the water as he brought his hand up. Sure enough, the dull glowing stone was still within it. Tony nodded to himself, closing his fist, and then moving up towards the surface. "I'll find Rhodey," He told himself,"He'll take me to the tower, and we'll find a way to fix this."

But when he finally breached the surface, with the cold air hitting his face, he saw only an open ocean. A frown graced his lips, turning his body to look the other way. Once again, there was nothing. Tony brought a hand up to scratch at his wet hair, confusion filling him. "I couldn't have been out for that long.. Right?" He asked himself.

He looked up, searching for any birds, or maybe even a mechanical suit. Once again, nothing. Tony felt his worry increase tenfold. _How am I supposed to get back?! How far am I from New York? What if this becomes permanent before I can?!_

Just as that panic was about to boil over, he heard a buzzing noise in the distance. He whipped his head around, and squinted. In the horizon, he saw.. _A boat!_ His heart jumped, and he quickly raised his hands, struggling to remain up on the surface as he yelled,"HEY! OVER HERE!"

After calling out for several seconds, he realized the boat was getting closer. He let out a huge sigh of relief, lowering his hands back into the water. As soon as the boat got close, Tony swam near the edge. Three faces looked over at him, none of which he recognized. But it didn't matter, he had a way home now.

He grabbed the side of the boat, and said,"I'm Tony Stark. I need your help. I have to get back to New York, it's very important. I can return the favor for you afterwards, but right now I have nothing to give you. Can you please help me?"

They looked at him in confusion, before exchanging looked with each other. After all the stress Tony had endured, this made him grow extremely frustrated. Please just let me on the boat! I want to go home!He frantically thought as they turned back towards him.

The middle one, a muscular man with a beard gave him a gentle smile, and reached out a hand. Tony sighed in relief, using his empty hand to grab it. They began to pull him up on the boat, much to Tony's happiness. But then, just as he was out enough to sit on the side, the woman with them let out an inhuman scream.

Tony jumped, turning to her. She was shakily pointing at his tail, as garbled nonsense escaped her. Tony grew worried, and held his hands up in a non-violent gesture. "W-wait! I don't want to hurt you! I'm human! I promise!"

But then the man pointed at him, frantically talking in the same garbled nonsense as the woman. Then, the small kid that was with them grew excited, exclaiming in the same blur of sound. It sounded like no language Tony had ever heard, and everything on the boat that could have been words looked like a blur. "I-I can't.. I can't understand them.. They can't understand _me_.." He realized in terror.

A sudden thump snapped Tony out of his daze, and he saw the man holding rope and a net. Instantly, Tony realized what was going on. "Wait!" He frantically cried,"I'm not a merman! I'm human! You're my only chance! _Please!_ Let's talk about this!"

But the man began to quickly advance, causing Tony to cry out. He threw himself off the side of the boat and back into the water, swimming as fast as his inexperienced tail would let him. The adrenaline that was flowing through him kept him going for what seemed like hours, until he was gasping every breath. Finally, he dove down into the waving seagrass below him in a desperate attempt to hide.

The genius quickly squeezed as far down as he could, flattening his tail against the ground. His whole body was shaking with nerves. _They weren't going to help me.. They wanted to tie me up and.. Oh god.. What were they going to do with me?!_

His eyes began to burn, and he brought his hands up, wrapping around his torso in a desperate attempt for comfort. He was afraid, nothing made sense, and he just wanted to go home. _But I can't… I'm stuck.. I'm trapped.._

If one could cry underwater, Tony knew he would be. But such a feat was impossible, so all he could do was curl up tighter, stare at the waving grass below, and wish for a way to escape the sadness clawing at his heart.

* * *

Steve hadn't been expecting a call so soon, even though it had already been six months since he had sent the phone. In all honesty, he never expected one at all. But sure enough, as he was laying quietly in his bed, the shrill ringing reached his ears.

Steve jumped, his heart slamming against his chest. His shaky hands quickly pulled up the phone from his bedside, softly whispering, "Stark." He ignored the instant fearful feelings in his heart, and answered it on speaker.

"Stark? What is it?" He answered professionally. There was a tense silence on the other side of the line, causing the super soldier to grow a bit annoyed. "This better not be a prank, Stark. What do you want?"

A sudden, familiar laughter echoed on the other side. "You know, when Tony told me he got a phone from you, I never thought we'd use it.. You bastard." He snarled, voice dripping with venom.

Confusion filled Steve at first, but was soon replaced with fear. "Colonel Rhodes?" He softly asked,"What… Where is Stark?"

"That is why I'm calling, Rogers," The man replied, his voice taking a somber tone. "Tony… Tony's gone. He was killed."

Steve felt the world swim, his breathing beginning to quicken, and body filling with shock, before he frantically asked,"But.. But how?"

Rhodey let out an angry growl. "It was another one of those stones, like the Tesseract. He tried to stop that bastard… There was an explosion.. All that was left was parts of his suit. He's gone."

Steve's whole body had gone cold, throat dry, and unable to respond. Rhodey realized this, and continued. "I still hate you, Rogers, nothing will change that. But Tony would want you to know what happened.. And that we don't know where the stone is. We're going to find it, whether you help or not," He snarled.

"We'll help!" Steve exclaimed, before sinking into his chair with a shaky breath. "We'll help… We'll do the best we can. We'll find who is behind this and we'll avenger Tony."

There was a long silence, before Rhodey firmly said,"Good. Maybe, for once, you'll actually _help_ Tony… Even though it's too late for that now." His voice suddenly hitched, shaking as the an began to cry. A few seconds after that heartbreaking noise entered his ears, he heard the dial tone that followed.

The phone fell from his frozen hand, clattering to the ground net to him. His eyes began to burn as large, wet tears tumbled down his cheeks. He leaned forward, and shakily whispered,"Oh god.. Tony.. No.."

Thoughts began to flow into his mind, as if a dam had just been broken. What if he had followed the accords? Would that man have attacked? What if he had tried to listen to Tony in Siberia? What if he tried to calm him down instead of fighting him? Then he would have been there… They all would have.

"W-we could have stopped him.. We could have saved you.. He whispered,"I-if I had been there.. Oh god, Tony!"

He buried his face in his calloused hands, his emotions catching up to him. He sobbed, biting his lips and fighting against the burning guilt flowing throughout isn't what he wanted at all, why did it have to end in such a way? _It's all my fault.. It's all my fault.._

The guilt throughout him suddenly began to be quenched, becoming filled with determination. "I'll avenge you, Tony," He declared,"We'll find whoever did this, and we'll make them regret ever hurting you. I promise."

What hurt the most though was that no matter what he did now, none of it would bring Tony back.


End file.
